The principle for ultraviolet rays irradiating fluorescent material to emit visible light is that when the ultraviolet radiation photons collide with fluorescent material atoms, the electrons are transited to a higher energy level, followed by the excited electrons returning to a lower energy level, releasing the energy in the form of low-energy photons in visible range.
Ultraviolet fluorescent ink is prepared by adding corresponding fluorescent compounds in the ink. A barcode printed with ultraviolet fluorescent ink cannot be seen (invisible) under natural light, or appears in colors that are different from those of conventional inks; while under ultraviolet rays, it shows a clear bright fluorescent patterns or unusual bright light. With different fluorescent materials, different wavelengths of ultraviolet light source and their interactions, the fluorescent patterns can appear in a variety of colors, such as red, yellow, green, blue and so on.
According to the appearance colors, the fluorescent inks can be classified as colorless, colored and color-changing fluorescent inks. A pattern printed with colorless fluorescent inks is invisible under natural light, while a clear bright fluorescent pattern with bright colors is showed under ultraviolet light. Colored fluorescent inks exhibit colors under natural light, while under ultraviolet light, the original colors shine to present fluorescent effects. Color-changing fluorescent inks show a color in natural light and another in ultraviolet light.
A barcode printed with ultraviolet fluorescent inks is advantageous in being invisible or difficult to see, which means it cannot be copied, thus it can be applied to the printing of the label, package, instruction book of bill, card, tobacco, wine, medicine, cosmetics, etc., which require high security, with a wide range of applications. Therefore, it is necessary to design a barcode reader device for reading the barcodes printed with ultraviolet fluorescent inks.